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EPA - Pyrethrins and Pyrethroids.
WIKIPEDIA - Pyrethroid.
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum).

Pyrethroids now constitute the majority of commercial household insecticides.[1] In the concentrations used in such products, they may also have insect repellent properties and are generally harmless to human beings in low doses but can harm sensitive individuals.[2] They are usually broken apart by sunlight and the atmosphere in one or two days, and do not significantly affect groundwater quality.[3] Mode of action[edit] Pyrethroids are axonic excitoxins, the toxic effects of which are mediated through preventing the closure of the voltage-gated sodium channels in the axonal membranes. The sodium channel is a membrane protein with a hydrophilic interior.

Over the last ten years, some resistance has been detected in Brazilian and Venezuelan triatomines (Vassena et al. 2000). Deltamethrin is commonly used for the chemical control of Triatoma infestansin several Latin American countries. In general, it is a very effective triatomicide, as recently shown by Rojas de Arias et al. (2004). Low pyrethroid resistance levels have also been found in several areas of Argentina (Vassena & Picollo 2003, González Audino et al. 2004).